First dump the factory head unit and replace it with something like this. There's no need to go overboard, not that you're going to with a $500 budget anyway.
http://www.crutchfield.com/p_105KDHDR60/JVC-KD-HDR60.html?tp=5684
I have the previous version and love it. Blows the doors off the Becker.
I chose it because:
- HD Radio built in; many stations now broadcast in HD.
- iPod & USB inputs on the face
- bluetooth connectivity
- illumination can easily be set to very closely match the factory dash lights, giving it a more factory look
Do your upgrades step-wise. I had big ideas for my system, but ultimately only did the head unit and dash speakers.